Two types of projectors are currently in use for the viewing of photographic slides, and these two types differ from each other essentially in the type of slide magazine used. One type uses a long magazine and the other type uses a circular magazine or carrousel. Long magazine projectors have a channel for lengthwise advancement of a long magazine, and include a driving pinion which extends into the channel and, with suitably disposed teeth, meshes with a rack or teeth provided on the long magazine. The long magazine is advanced one compartment at a time by stepwise rotation of this driving pinion. For injecting individual slides or slide frames into the optical channel of the projector, a gripping element generally is provided which grips a slide in its rest position and draws or pushes the slide sideways out of its compartment in the long magazine and into the optical channel of the projector. After the slide has been viewed, it is returned sideways into its associated compartment in the long magazine by the gripping element.
Usually, instead of gripping elements, round magazine projectors use a so-called chute, through which a slide in the proper position falls into the optical channel and is returned to the magazine by a lifting mechanism after the slide is viewed.
Long magazine projectors are already known in which a round magazine can be employed in place of a long magazine. In such projectors, the round magazine is placed upright in the long magazine channel and the drive mechanism and the gripping elements are designed so that the round magazine is moved stepwise by the driving pinion and the slide or slide frame is transferred into the optical channel of the projector by the gripping element.
Prior to this invention, it had not been possible to use long magazines with round magazine projectors, which are preferred to the long magazine projectors since they have a simpler construction and are cheaper. The reason this was impossible was because of the special configuration of the drive element for the round magazine found in the round magazine projector which makes it impossible to transfer the individual slides out of a long magazine and into the optical channel of the projector.